A rotation support apparatus fitted with a rotational speed sensing device is used, for example, for rotatably supporting wheels of automobiles relative to a suspension system, or supporting a rotation shaft constituting an automotive transmission in a housing, as well as for detecting a rotational speed of the rotating portion.
For example, in the case of the automotive transmission, it is necessary to detect the rotational speed of a rotation shaft to determine the gear shift timing. Moreover, in the case of an automobile, it is required to detect the rotational speed of wheels to properly control an anti-lock brake system (ABS) or a traction control system (TCS).
Therefore, there has heretofore been widely used, a rolling bearing unit fitted with a rotational speed sensing device for rotatably supporting a rotating portion such as a rotation shaft and wheels which constitute various mechanical devices, relative to a fixed portion such as a housing or a suspension system which does not rotate at the time of use, as well as for detecting the rotational speed of the rotating portion.
As a rolling bearing unit fitted with a rotational speed sensing device which can be used for such an application, there is known the device as disclosed in Japanese Laid Open Patent Publication No. TokuKaiHei 7-311212. The rolling bearing unit fitted with a rotational speed sensing device described in this publication rotatably supports an inner ring that is a rotating ring on the inner diameter side of an outer ring that is a stationary ring, via a plurality of rolling members specifically balls.
Moreover, an encoder is supported on an outer peripheral surface on an end portion of the inner ring, and a sensor carrier holding a sensor is supported on an end portion of the outer ring.
In this state, a detecting section of the sensor is made to face a portion to be detected of the encoder across a small gap spanning in the axial direction. The sensor carrier is securely supported on the outer ring in the state that positioning thereof in the axial direction is performed by internally fitting and securing a cylindrical portion disposed at the base end thereof on an end portion of the outer ring, and abutting a part of the sensor carrier against the end face of the outer ring.
At the time of using the rolling bearing unit fitted with a rotational speed sensing device, for example, the outer ring is internally fitted and secured to a stationary member such as a housing or the like, and the inner ring is externally fitted and secured to a rotating portion such as a rotation shaft or the like.
When the inner ring rotates in this state, the output from the sensor whose detecting section is facing the portion to be detected of the encoder via the small gap, changes. The frequency at which the output from the sensor changes is proportional to the rotational speed of the inner ring. Hence, if a signal representing the output is sent to a control device via a harness which is guided out from the sensor, the rotational speed of the rotating portion can be obtained.
If the rolling bearing unit in which the outer ring that is a stationary ring is pressed into and internally fitted inside the housing that is a stationary member is used, there may be cases where the friction force acting on a fitting face between the housing and the outer ring is insufficient, or where a small gap occurs in a part of the fitting face between the housing and the outer ring, due to a change in interference dimensions in the fitting portion, because of a temperature difference between the housing and the outer ring, or an elastic deformation on the fitting face. As a result, there is the possibility that so-called creep occurs where the outer ring rotates relative to the housing at the time of use. If such creep occurs in a standard rolling bearing (having no rotational speed sensing device), there is no major problem.
When a sensor is supported on the outer ring however as with the rolling bearing unit fitted with a rotational speed sensing device, the sensor can rotate relative to the housing, together with the outer ring, As a result, there is the possibility of the harness for taking out the output signal from the sensor being strongly pulled or wound up on peripheral members and severed so that the rotational speed cannot be detected. Moreover, even if the harness is not severed, but rotation of the sensor occurs, accurate detection of the rotational speed cannot be performed.
In U.S. Pat. No. 5,622,437, there is disclosed a rolling bearing unit for supporting wheels in which a part of a sensor carrier supporting a sensor is located by being clamped between an outer ring that is a stationary ring, and a part of a knuckle that is a stationary member in which the outer ring is internally fitted and secured, so that the sensor is located in position. Even in the case of such a rolling bearing unit for supporting wheels however, when rotation of the outer ring occurs inside of the knuckle, there is the possibility of the sensor carrier supporting the sensor rotating together with the outer ring, due to its being clamped by means of a friction force between the end face of the outer ring and the sensor carrier. Hence, as in the above described case, there is also the possibility of the harness being severed, or the accurate detection of the rotational speed cannot be performed.
To solve the above described problems therefore, the occurrence of the above described creep has heretofore been prevented by spanning a pin between the outer ring that is the stationary ring and a housing or the like that is a stationary member, or connecting the outer ring and the housing by a key.
However, providing a portion or member separately for preventing creep gives rise to an increase in cost, which is not desirable. It is therefore desired to realize a structure which can solve the above problems, without increasing the cost.
On the other hand, in the case of the above described conventional structure, since a harness is attached to the sensor, the operation of fitting the rolling bearing unit inside of the machinery must be performed with care so that the harness is not caught in a fitting portion between the outer ring and the housing, or in a fitting portion between the inner ring and the rotation shaft. Particularly, when the sensor and the harness are integrally connected in advance, in the case where the harness attached to the sensor is long, extra care must be taken since the harness can be easily caught in the above described fitting portions. Therefore, the operation of fitting the rolling bearing unit becomes more difficult due to this extra care requirement.
When the rolling bearing unit is fitted inside of the machinery, if the operation of fitting the rolling bearing unit with the encoder inside of the machinery, and of fitting the sensor carrier with the sensor inside of the housing can be carried out separately, then the fitting operation for the rolling bearing unit can be facilitated.
For example, in the case of a construction where the sensor and harness as separate bodies are connected in a subsequent stage, i.e. if an operation for internally fitting and securing the sensor carrier to the housing, and an operation for connecting the harness to the sensor supported on the sensor carrier are carried out before incorporating the rolling bearing inside of the machinery, since the work space inside the housing is relatively secure, the fitting operation of these members can be facilitated. Moreover, subsequently at the time of fitting the rolling bearing inside of the machinery, the operation for ensuring that the harness is not caught in the above described respective fitting portions can be facilitated.
In the case of the above described conventional construction however, since the constriction is such that the rolling bearing and the sensor carrier have to be fitted at the same time, the fitting operation cannot be facilitated as described above.